Kinetics of the Thermal Transition of Carbamazepine Polymorphic Forms in the Solid State

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Abstract
The thermal transition of carbamazepine polymorphic forms (forms I, II and III) in the solid state was investigated by X-ray powder diffractometry. From the kinetic analysis according to the method of Hancock-Sharp, it appears that the transition of form I to form III follows the mechanism of random nucleation and 2-dimensional growth of nuclei (Avrami-Erofeev equation). The activation energy for the transition from form I to form III was 54.7 kcal/mol from the slope of the Arrhenius plots. The transition of form II to form III will proceed by the mechanism of the 2-dimensional diffusion. The activation energy for this transition was calculated to be 31.6 kcal/mol.

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